Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-03-03
2002-09-24
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06456406
ABSTRACT:
The present invention relates to a transparent communication network for optical-signal transmission, having a ring-shaped structure, comprising a double communication line and nodes located along the line for adding and dropping signals related to one or more communication channels, from and into the ring respectively.
In the network, generally along optical fibres, signals corresponding to different channels, each having a different wavelength, travel together, according to the so-called wavelength division multiplexing (or WDM) technique. The components of one signal having a wavelength corresponding to one channel are dropped from the network and added thereinto in an optical form, at the nodes. The network enables transmission of optical signals without intermediate conversions to the electric form and it is therefore transparent to the particular structure of the elementary information to be transmitted (usually electric signals in a digital form).
In optical-signal transmitting networks the amount of the exchanged information is very high. For this reason, a failure can have very severe consequences in that a very high number of subscribers can be deprived of the information flow.
Typical failures may be breaking of an optical fibre, because said fibre can be, for example, accidentally cut by operators not aware of the presence of same, and a cutoff in the operation of the whole node, due for example to a fire, lack of electric energy or failure of one component.
In order to face such a situation in an automatic manner and within sufficiently short periods of time so that the information flow is not interrupted, self-healing-ring networks have been conceived.
In these networks the different nodes are connected with each other- by two optical-fibre lines, closed upon themselves to form a ring: a primary ring line (also referred to as external or working ring) and a secondary ring line (also referred to as internal or protection ring). Under normal conditions signals travel in one direction alone on the primary line and are dropped from and/or added into the different nodes depending on the wavelength.
In the case of a node failure, or breaking of a primaryline optical fibre between an upstream and a downstream node, continuity is restored by diverting the signal flow from the primary to the secondary line in the node which is upstream of the breaking (with respect to the signal travel direction in the primary line) and from the secondary to the primary line in the downstream node. In the secondary line, signals travel in the opposite direction with respect to the primary line. In order to perform these diversions in an automatic manner from one ring line to another, two so-called “2×2” directional switches are provided for use in the nodes, which directional switches are optical four-way components having two inputs and two outputs. In a normal configuration, the first output is optically connected to the first input and the second output is optically connected to the second input, whereas in a switched-over configuration the first output is optically connected to the second input and the second output is optically connected to the first input.
A node of this type is described for example in an article by S. Merli, A. Mariconda and R. de Sanctis entitle “Analisi e dimensionamento di un anello ottico trasparente per sistemi D-WDM, con funzioni di riconfigurazione automatica in caso di rottura dell'anello e di Drop-Insert locale dei canali” (Analysis and dimensioning of a transparent optical ring for D-WDM systems having functions of automatic reconfiguration in case of ring breaking and local Drop-Insert of the channels), Atti del Convegno FOTONICA '95 (FOTONICA '95 Meeting Records), Sorrento, IT, May 1995. It enables signals to be diverted to the secondary ring line in case of breaking of the primary ring line. In addition, it enables the optical user unit of the node (typically a wavelength-selective optical switch, for adding and dropping the signals of a channel having a predetermined wavelength) to be bypassed in case of failure of same, while saving transmission between the remaining network nodes.
Networks of this type require a central unit capable of recognizing and localizing an occurred failure (for example, through signaling of the lack of signal by the node located downstream of the failure, which can carry out switching of the optical signal to the service line in a self-governing manner) and of sending to the node upstream of the failure, the switching-over command so that it can receive signals from the service line. For this reason it is necessary for the central unit to communicate with each of the nodes, also and above all in case of failure in the communication line. Therefore emergency lines for connection between the nodes and the central unit need to be arranged, which lines must be independent of the ring line for communication between the nodes. These emergency lines (that can be optical, electrical, or radio link lines or lines of any other type) together with the central unit involve an important complication in the communication network.
In addition, in network architectures of the above stated type, the time necessary for transmitting the information about the occurred failure to the central unit, processing the information by said unit and transmitting the switching over command to the node upstream of the failure is to be added to the intervention time by the directional switches, establishing the overall time for recovery of the network functionality after a break. This overall recovery time can be much higher than the intervention time of a directional switch, presently reaching values on the order of some milliseconds in switches of the acousto-optical or magneto-optical type or some tens of milliseconds in switches of the mechanical type.
An optical self-healing-ring network is also described in an article “A uni-directional self-healing ring using WDM technique”, by E. Almstrom et al., ECOC '94 Conference Proceedings, Florence, IT, 25-29 Sep., 1994, vol. 2, pages 873-875. The optical network contemplates the use in the nodes of optical switches having more than one input and more than one output. The network is shaped so that the nodes can close the ring on the protection fibre, as soon as they detect a break along at least one of the fibres.
According to one aspect, the present invention relates to an optical self-healing-ring communication network comprising:
one optical communication line forming a first closed optical path;
at least two optical-signal add/drop nodes optically connected along said optical communication line;
a second optical communication line forming a second closed optical path and optically connected to said optical-signal add/drop nodes;
in which at least one of said nodes comprises controlled selection means for selectively dropping said optical signals from one of said first and second communication lines,
wherein at least one of said optical-signal add/drop nodes further comprises means for the simultaneous input of at least one optical signal into said first communication line and into said second communication line.
In particular, defined in the optical ring communication network is a first and a second travel direction of said optical signals relative to the position of said optical-signal add/drop nodes, said first and second directions being opposite to each other and said network comprises means for the simultaneous input of at least one optical signal in said first direction along said first communication line and in said second direction along said second communication line.
Preferably the optical ring communication network comprises one pair of optical-signal add/drop nodes, optically connected with each other, in which the signals transmitted between the nodes of said first pair have a first wavelength, and at least one of said first and second optical paths comprises a second pair of optical-signal add/drop nodes, optically connected with each other, the signals transmitte
Arecco Fulvio
Brandao Sanches Marcos Antonio
Meli Fausto
Cisco Photonics Italy S.r.L.
Pascal Leslie
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